Getting different grips for your Police Positive Special may be difficult.

259XXX was made in 1922.
These older guns used a long grip frame with a square butt.
Most of todays grip makers only offer grips for the 1965 and later frame that has a short, stubby grip frame under the wood.
These grips overlap on the bottom of the short frame to give a full size grip.
These types will not fit your older model PPS, and most grips that are available for your gun will be replicas of the original, not larger.

Eagle Grips do make walnut grips for your model, but these too are the same size as the original.
Pachmayr, Hogue and most other makers will offer nothing for your gun at all.

About the only choice is to find a custom maker who will make you a true custom grip, or use a grip adapter like rodfac shows above.